Fillet weld strength table
Allowable load per inch of length for equal-leg fillet welds made with E70 electrodes, using the AISC allowable shear stress. Multiply by the weld length to size a connection, or compare against the load it must carry.
Allowable load, E70 electrode (21 ksi shear)
| Leg size | Throat (in) | Allowable load (kip/in) |
|---|---|---|
| 1/8 in | 0.088 | 1.86 |
| 3/16 in | 0.133 | 2.78 |
| 1/4 in | 0.177 | 3.71 |
| 5/16 in | 0.221 | 4.64 |
| 3/8 in | 0.265 | 5.57 |
| 7/16 in | 0.309 | 6.50 |
| 1/2 in | 0.353 | 7.42 |
Capacity comes from strength equals 0.707 times leg times length times the allowable shear stress. For E70 weld metal the allowable shear is 0.30 times 70 ksi, or 21 ksi (allowable stress design). For load-and-resistance-factor design, the available strength is roughly 1.5 times these values. The base metal at the joint must also be checked, since it can govern.
Need the minimum size or to read the symbol?
See the Weld Size Reference and the Welding Symbols Chart.
How to use the table
Find the load your joint must carry, divide by the allowable load per inch for the weld size, and you get the length of fillet required. A 1/4 inch E70 fillet carries about 3.71 kip per inch, so a 10 kip load needs roughly 2.7 inches of weld, split between both sides of the joint. Always check that the connected base metal can also take the load.
Electrode strength and design method
The 70 in E70 is the weld metal tensile strength in ksi. Higher-strength electrodes raise capacity proportionally. These figures use allowable stress design with a 21 ksi shear value; modern AISC load-and-resistance-factor design gives a higher available strength for the same weld, about 1.5 times, because it applies factors differently.
FAQ
How strong is a 1/4 inch fillet weld?
About 3.71 kip per inch of length with E70 electrodes under allowable stress design, from 0.707 times the leg times 21 ksi.
How do I calculate fillet weld length?
Divide the load by the allowable load per inch for the weld size. A 1/4 inch fillet at 3.71 kip per inch needs about 2.7 inches to carry 10 kip.
What does E70 mean for weld strength?
The weld metal has a 70 ksi tensile strength. The allowable shear used for design is 0.30 of that, or 21 ksi.